The present invention relates to a method of driving a luminescent display which can perform picture displaying with the use of an organic EL (Electro Luminescent) unit.
There has been known a conventional luminescent display which can perform picture displaying with the use of a plurality of luminescent units such as organic EL units. Such kind of conventional luminescent display includes a plurality of anode lines and a plurality of cathode lines, arranged in a matrix array to form a lattice pattern. A plurality of luminescent units are connected at a plurality of intersections formed by the anode lines with the cathode lines.
Each luminescent unit connected at one of the above intersections may be represented by an equivalent circuit shown in FIG. 7, including a light emitting element E having a function as a diode, and a condenser device C connected to the element E. In this way, such a luminescent unit can emit a light only when an electric current flows in a forward direction through the light emitting element E (functioning as a diode).
Further, as shown in FIG. 6, each luminescent unit includes a transparent substrate plate 101, successively laminated on the transparent substrate plate 101 is an anode (transparent electrode) 102, a luminescent layer 103, a cathode (metal electrode) 104. Once an electric current serving as a driving source is supplied to the anode 102 and the cathode 104 is connected to the earth, the electric current will flow through the luminescent layer 103, thereby enabling the luminescent unit to emit a light.
However, with the above-discussed conventional luminescent display, if the luminescent layer 103 involves a small-thickness portion or if the luminescent layer 1033 is partially so thin that it fails to serve as a separator between the anode 102 and the cathode 104, a problem called short circuit will occur between the anode 102 and the cathode 104, causing a leaked current and hence failing to enable the luminescent unit to emit a light in a predetermined desired manner.
In more detail, if the luminescent layer 103 involves a small-thickness portion, an electric resistance will become small at this portion so that a driving current will be collected in this small-thickness portion, resulting in a problem that there will be only a small electric current flowing through other portions of the luminescent layer 3, and hence causing a low light emission brightness on other portions of the luminescent layer 103.
Further, a short circuit will affect other luminescent units on an identical cathode line, causing the entire display to be unable to clearly display a picture.
It is an object of the present invention to provide an improved luminescent display capable of greatly reducing inferior luminescence as compared with a conventional display, so as to solve the above-mentioned problems peculiar to the above-mentioned prior art.
According to a first aspect of the present invention, there is provided a method of driving a luminescent display, said display including a plurality of anode lines and a plurality of cathode lines, a plurality of luminescent units connected at a plurality of intersections formed by the anode lines with the cathode lines, the anode lines (or the cathode lines) being used as scanning lines while the cathode lines (or the anode lines) being used as driving lines, in a manner such that when the scanning lines are being scanned, some of the driving lines are connected to driving sources in accordance with such scanning, so as to enable the luminescent units to emit lights, said method being characterized in that: during a predetermined period, a reverse voltage having a direction opposite to that of a voltage to be applied for light emission of a luminescent unit, is applied to each luminescent unit.
According to a second aspect of the present invention, there is provided a method of driving a luminescent display, said display including a plurality of anode lines and a plurality of cathode lines, a plurality of luminescent units connected at a plurality of intersections formed by the anode lines with the cathode lines, the anode lines (or the cathode lines) being used as scanning lines while the cathode lines (or the anode lines) being used as driving lines, in a manner such that when the scanning lines are being scanned, some of the driving lines are connected to driving sources in accordance with such scanning, so as to enable the luminescent units to emit lights, said method being characterized in that: the driving lines are connected to the driving sources when the luminescent units are caused to emit lights, but connected to an earth potential when the luminescent units are not caused to emit lights; the scanning lines are connected to earth means when the scanning lines are scanned, but connected to a constant voltage source when the scanning lines are not scanned; during a predetermined period, a reverse voltage having a direction opposite to that of a voltage to be applied for light emission of a luminescent unit, is applied to each luminescent unit.
In the second aspect of the present invention, the reverse voltage is applied by connecting the scanning lines to the constant voltage source and connecting the driving lines to the earth potential.
According to a third aspect of the present invention, there is provided a method of driving a luminescent display, said display including a plurality of anode lines and a plurality of cathode lines, a plurality of luminescent units connected at a plurality of intersections formed by the anode lines with the cathode lines, the anode lines (or the cathode lines) being used as scanning lines while the cathode lines (or the anode lines) being used as driving lines, in a manner such that when the scanning lines are being scanned, some of the driving lines are connected to driving sources in accordance with such scanning, so as to enable the luminescent units to emit lights, said method being characterized in that: the driving lines are connected to the driving sources when the luminescent units are caused to emit lights, but connected to an earth potential when the luminescent units are not caused to emit lights; the scanning lines are connected to earth means when the scanning lines are scanned, but connected to a constant voltage source when the scanning lines are not scanned; during a predetermined period from the end of a scanning of one frame until a shift into a scanning of a next frame, a reverse voltage having a direction opposite to that of a voltage to be applied for light emission of a luminescent unit, is applied to each luminescent unit.
In the third aspect of the present invention, during said predetermined period, each of the scanning lines is connected to a constant voltage source, while each of the driving lines is connected to an earth potential. Further, said predetermined period is allowed to be equal to a scanning period of one scanning line.
According to a fourth aspect of the present invention, there is provided a method of driving a luminescent display, said display including a plurality of anode lines and a plurality of cathode lines, a plurality of luminescent units connected at a plurality of intersections formed by the anode lines with the cathode lines, the anode lines (or the cathode lines) being used as scanning lines while the cathode lines (or the anode lines) being used as driving lines, in a manner such that when the scanning lines are being scanned, some of the driving lines are connected to driving sources in accordance with such scanning, so as to enable the luminescent units to emit lights, said method being characterized in that: the driving lines are connected to the driving sources when the luminescent units are caused to emit lights, but connected to an earth potential when the luminescent units are not caused to emit lights; the scanning lines are connected to earth means when the scanning lines are scanned, but connected to a constant voltage source when the scanning lines are not scanned; during a predetermined period from the end of a scanning of one scanning line until a shift into a scanning of a next scanning line, a reverse voltage having a direction opposite to that of a voltage to be applied for light emission of a luminescent unit, is applied t~o each luminescent unit.
In the fourth aspect of the present invention, during said predetermined period, each of the scanning lines is connected to a constant voltage source, while each of the driving lines is connected to an earth potential.
According to a fifth aspect of the present invention, there is provided a method of driving a luminescent display which includes a plurality of luminescent units adapted to be selected for light emission, so as to display an image, said method being characterized in that: at a moment when an electric power is supplied to the luminescent display, a reverse voltage having a direction opposite to that of a voltage to be applied for light emission of a luminescent unit is applied to each luminescent unit.
In any one of the above first to fifth aspects of the present invention, each of the luminescent units has a diode characteristic which can perform a light emission only in response to a voltage applied in one direction.
Further, in any one of the above first to fifth aspects of the present invention, each of the luminescent units contains an organic EL (electro luminescent) material.
The above objects and features of the present invention will become better understood from the following description with reference to the accompanying drawings.